SITE INFORMATION AND CORRESPONDENCE_CASE 1

Home Browse Search

Discussions with laboratory analysts and remediation engine.,.-Ts indicate that itis widely believed that the gmaccst number of false positives will occur when low concentrations (<100 ug/L) Ivfl'BE are reported by EPA 8020_ This is sugported by recent studies by Mobile Oil and Shell Development Company which predict thaz false positive detections of MTBE will tend to oc.-.= when <20-50 ug/L.co'ncerstradcas of MTBE ane repotted by EPA method 8020: The data analyzed in this report strongiy contradict these expectations. The reported EPA SM values for the 2 false:positives in this data set are 240 and 5300 ug/L. Therefore, presently. the reported EPA 8= concentration (above 20`iig/I-) have ao predictive value for indicating the probability of false positive mis-idt=tifications_ New samples were obtained nom the well previously repordn a false oositive EP of 5300 ug/L. Bah GC/PID and GC/,MS anal g A 8020 value ysis perr"ozmed,ar Lawrez ce Livermore Nadonal Laboratory al.NL) conf=ied ND Ievels of MTBE. Our analysis also couzfmza�ed the presence o£ 3etection ornrane, a ga.Soline carrzgotmemmt which can caelum with MTBE.leadinj rn false detection or overestimation of MTBE concentrations by EPA 8020. 3-me:hylpemmne was also indeaenderdy demcmd in these samples by Shell Development Company research laboratcuies. been mi a, this czamQle shows that gasoline c0MV0n rets present in LLAT ground water have been us-idcntiiied as:MTBE by EPA 8020 analysis. Other laboratories have reported that the presence of 2-methylpenr2ne in LUFI`ground water;samples can result in false detection of MZBE_ Therzfom, we suggest that analytical lab 'oratories perform an "inte fenmce died:" analysis of a 3-rnethylpentane and 2-rnethyipentatie standards in the presence and absence of MTBE to cYaluate,�whether this compound co-elutes with MTBE under routine conditions used in their laboratory for EPA 8020"analysis. It is our opinion that as.analyatal laboratories optimize conditions to detect and,quantify MTBE by EPA 8070 in the prseaca of 3- and 2-methyl both the false nvsuives,will decrz3se. In addition e' she number crud coat.-ra=don of use of a sin 1e column f cheat Stare of California reg*.mlations regnhe Association f C.slifo=ia Testing nier maples containing gasojine. The confirmation column for duction of WME is rh�Bs has rhe�Use of a second number of false positives detected by EPA 8024 (d FE nS vol.gasoline sue 3,my 199 ). Be the the auadrY of EPA 8020 data may improve due to optirnizarions of GC/PID separation �3ecanse conditions armdlor the use of it second column, we re mmmeud d=a comparzsoaof E.oA $020 and 8240 data should be performed in the fumm to evaluate whether trends frorrm!thzs darn. sat continue. Agreement of analytical values reported for EPA 8020 and EPA 87�t0: For our analysis, RPD values greater thea 40% are-_ unaccevtabl deWorusand a r the values obtained by these tyro anal g ��t dizrere=c between analytical methods. We reviewed th=e classes of�lTBE dare samples with ND or low;concentrations of gasoline cointuounds, samples with h g t concentrations of gssalinc and Iow couceatradaas of,rME, armd samples wir;:t both Izigh concentrations of gasoline and MTBE. L-1 gene:=/, we found averment between the MTBE c6nc:rnttations reportzedby bath anethods was fair for the 48 samples that did not contain elevate conc"mtrations of gasoline cam 27 had RPD v�neS greater than 40 , (13 of 48 samples cmuainiug ND to 7- ugTL � and/or 7 ug/L B compounds). lrne=tingly,in the majority of TrX these cases (9 out g/ BB the MI=E concenmazion z�epormd by EPA 8Q20 was significantly lowe<than the:es o re EPA 8240. We have no exp[anation as to why Epi $02U would teed to produce a ported by anaIxtic'al value than EPA 8240 in $pprozYma.tely 19% or the samples that do not contain elevated cancenirations-'Of gasoline compounds. Only 3 samples contained clevazcd concena-ations of gasoline compounds (1372.X and/or 3 compounds at cax:cenzrauons greater or equal to 200 ug/L) and low c nr-.eons of\,=E (20- 2